This invention relates to a process for the activation of supported Fischer-Tropsch catalysts that enhances their activity and/or selectivity in the production of higher hydrocarbons from synthesis gas.
The conversion of synthesis gas, i.e. carbon monoxide and hydrogen, to higher value products is well known and has been in commercial use for many years. Typical processes include, for example, methanol syntheses, higher alcohol synthesis, hydroformylation and Fischer-Tropsch synthesis. The synthesis gas mixture is contacted with a suitable catalyst typically comprising at least one Group VIII metals. Suitable Fischer-Tropsch catalysts comprise one or more catalytic Group VIII metals, such as iron, cobalt and nickel. For oxygenate synthesis, copper may be included as well.
There exist many variations of the formulation and preparation of catalysts useful for the conversion of synthesis gas. In general, the catalysts are classified into two broad types, unsupported metals, known as Dispersed Active Metals and a larger groups of catalysts metals supported on refractory oxides, such as silica, alumina, titania or mixtures thereof. Such catalysts, whether supported or unsupported may be enhanced by the addition of other metals or metal oxides, known as promoter metals.
Supports for catalyst metals are generally pilled, pelleted, beaded, extruded, spray-dried or sieved materials. There are many methodologies reported in the literature for the preparation of supported catalyst metals. Examples of such techniques include incipient wetness impregnation, slurry impregnation, coprecipitation, and the like. It will be appreciated that high metal loadings are generally obtained by coprecipitation or multiple, i.e. two or three, impregnations, whereas low metal loading catalysts may be prepared utilizing a single impregnation. The catalyst metal content of such catalysts may vary from one to fifty weight percent. Promoter metals or metal oxides may be added during the impregnation steps using soluble salts of the respective metals such as Pt, Pd, Rh, Ru, Os, Ir, Mo, W, Cu, Si, Cr, Ti, Mg, Mn, Zr, Hf, Al, Th and the like.
It will further be appreciated that the choice of a particular metal combination and the amount thereof to be utilized will depend upon the specific application used in the conversion of synthesis gas. When a suitable support has been impregnated with one or more metals as by impregnation to form a catalyst precursor, it may be dried and then calcined in an oxygen-containing environment. The precursor is thereafter activated by reduction at elevated temperature in the presence of a reducing gas, typically containing hydrogen. Optionally, the catalyst is activated by contacting with hydrogen gas in presence of liquid hydrocarbons as disclosed in U.S. Pat. No. 5,292,705.
Regardless of the particular formulation and method of preparation, the method of activation, which may include a pretreatment, impacts the productivity and/or selectivity of the catalyst. Selectivity is generally expressed in terms of the percent of an undesirable substance in the product mix. For example, methane selectivity in a Fischer-Tropsch reaction is the percent of methane formed with the desired higher hydrocarbons. If productivity is often tied to a specific catalyst synthesis method or catalyst activation method, low productivity may also result from problems that may occur during the activation process itself. For example it is well known that the reduction of cobalt containing catalyst under conditions in which high partial pressure of water are obtained, lead to a poor catalyst activation and low catalyst productivity. In some cases, such poorly activated catalysts, which cannot be used at all, are discarded and then treated for metal recovery. It is obviously commercially significant to provide a method for the activation of catalyst that boosts the productivity and selectivity of catalysts, especially poorly activated catalysts, thereby avoiding the significant expense of their disposal.
Typically, metal containing catalysts are activated by treatment at elevated temperatures in presence of a reducing gas, for example a hydrogen-containing gas. In some specific applications such hydrogenation reactions for specialty chemicals, the metal component of the catalyst may be reduced at lower temperature using other reducing reagents such hydrazine or alkyl aluminum to maximize the metal dispersion or catalyst activity. Formation of a reduced catalyst may also be achieved by direct decomposition of metal salts, for example, thermal decomposition of oxalates. Carbon monoxide hydrogenation catalysts are commonly activated by means of high temperature reduction in presence of a hydrogen-containing gas. Typical procedures ensure a low partial pressure of water during the reduction by controlling the rate of reduction of the metal oxides. There are known pretreatment methods described in the literature.
U.S. Pat. Nos. 4,492,774; 4,595,798; 4,088,671; 4,605,679; and 4,670,414 and EP 0 253 924 disclose a method of activation of cobalt catalysts by means of a reduction/oxidation/reduction (Rxe2x80x94Oxe2x80x94R) cycle, resulting in an increase in activity for Fischer-Tropsch synthesis. To our knowledge, all the oxidation/reduction or reduction/oxidation/reduction cycles described in the above patents, were effected by treating a dry solid catalyst with an oxygen-containing gas at high temperature, resulting in the formation of the most stable oxide i.e., Co3O4. Several of these citations stressed the importance of controlling the exothermicity of the oxidation reaction and ensuring a low partial pressure of water during the reduction to avoid sintering of the cobalt particles, which may be detrimental to the activity of the final catalyst.
Khodakov et al. In a paper in Oil and Gas Science and Technology Rev. IFP, 54, 525 (1999) teach that contacting a reduced cobalt catalyst with water, followed by drying and calcining in air results in the formation of smaller cobalt oxide crystallites relative to those that would be formed by decomposition of the initial cobalt salts.
It is generally recognized that the economic worth of a given catalyst is a function of its original cost and its activity. It is apparent from the foregoing discussion that there has been considerable effort going back over many years to improve the economic worth of catalysts, since a process that will effectively increase the activity of a catalyst and/or extend the useful life will significantly improve the worth of that catalyst. Such a process is provided in accordance with the present invention.
In accordance with the present invention, catalytic activity and/or methane selectivity of supported Fischer-Tropsch metal catalysts or catalyst precursors are enhanced by a process comprising initially reducing with a hydrogen-containing gas at elevated temperatures to cause at least part of the metal therein to be in the metallic state, impregnating under a non-oxidizing atmosphere with a solution of at least one member selected from the group consisting of ammonium salts, alkyl ammonium salts and weak organic acids, optionally in combination with ammonia, oxidizing in the presence of the impregnating solution at low temperatures and reducing with a hydrogen-containing gas at elevated temperatures to activate the catalyst. Optionally, the supported catalyst precursor is calcined in the presence of an oxidant-containing atmosphere prior to activation. The activated catalyst may also be passivated to further enhance its properties.
Supported metal catalysts, which correspond essentially to reduced metals formed by one of the recognized techniques discussed above onto a suitable support structure, typically a refractory inorganic oxide, such as titania, silica, silica-alumina, aluminum and the like, are utilized in a broad range of applications such as hydrogenation of hydrocarbons and carbon monoxide. Titania is a preferred support material for the catalyst metal substrates treated in accordance with the present invention. Start-up procedures for such reactions, which may include specific activation sequences, are highly dependent upon the catalytic reaction, the process design and, in particular, the reaction vessel design and configuration. The slurry bubble column reactor, is a preferred vessel for carrying out carbon monoxide hydrogenation reactions. The use of slurry bubble column for CO hydrogenation is particularly convenient in combination with the catalyst regeneration process of the present invention. In such reactors, the solid phase catalyst is dispersed or held in suspension in a liquid hydrocarbon phase by a gas phase, which continuously bubbles through the liquid phase. Supported catalysts useful for such applications contain at least 5 wt. %, preferably from 10 to 50 wt. %, of the catalyst metal in the reduced metallic form. Preferably, the catalyst comprises one or more of Co, Ni, Cu, Ru, Rh, Pd, Os, Ir, Re and Pt.
In the carbon monoxide hydrogenation reaction, syngas comprising a mixture of hydrogen and carbon monoxide is contacted with the catalyst thereby being converted into liquid and gaseous products, preferably C10+ liquid hydrocarbons, with shifting or non-shifting conditions, preferably the latter, wherein little or no water gas shift takes place. This hydrocarbon synthesis (xe2x80x9cHCSxe2x80x9d) process is generally carried out at temperatures of from about 160xc2x0 C. to 260xc2x0 C., pressures of from about 1 atm to about 100 atm, preferably from 10 atm to 40 atm, and gas space velocities of from about 100V/Hr/V to about 40,000V/Hr/V, preferably from about 1,000 V/Hr/V to about 15,000V/Hr/V. The expression xe2x80x9cV/Hr/Vxe2x80x9d represents the standard volumes of gaseous carbon monoxide and hydrogen mixtures at 25xc2x0 C. and 1 atm per hour per volume of catalyst, respectively. The molar ratio of hydrogen to carbon monoxide in the syngas feed is about 2.1:1 for the production of higher hydrocarbons. This ratio may vary to from about 1:1 to 4:1, and preferably is from about 1.8:1 to 2.2:1. These reaction conditions are well known and a particular set of reaction conditions can readily be determined from the parameters given herein. The hydrocarbon-containing products formed in the process are essentially free of sulfur and nitrogen-containing contaminants.
The hydrocarbons produced in a process as described above are typically upgraded to more valuable products by subjecting all or a portion of the C5+ hydrocarbons to fractionation and/or conversion. By xe2x80x9cconversionxe2x80x9d is meant one or more operations in which the molecular structure of at least a portion of the hydrocarbon is changed and includes both non-catalytic processing, e.g. steam cracking, and catalytic processing, e.g. catalytic cracking, in which the portion, or fraction, is contacted with a suitable catalyst. If hydrogen is present as a reactant, such process steps are typically referred to as hydroconversion and variously as hydroisomerization, hydrocracking, hydrodewaxing, hydrorefining and the like. More rigorous hydrorefining is typically referred to as hydrotreating. These reactions are conducted under conditions well documented in the literature for the hydroconversion of hydrocarbon feeds, including hydrocarbon feeds rich in paraffins. Illustrative, but non-limiting, examples of more valuable products from such feeds by these processes include synthetic crude oil, liquid fuel, emulsions, purified olefins, solvents, monomers or polymers, lubricant oils, medicinal oils, waxy hydrocarbons, various nitrogen- or oxygen-containing products and the like. Examples of liquid fuels includes gasoline, diesel fuel and jet fuel, while lubricating oil includes automotive oil, jet oil, turbine oil and the like. Industrial oils include well drilling fluids, agricultural oils, heat transfer oils and the like.
In accordance with the present invention, significant enhancement in both the productivity and methane selectivity for Fischer-Tropsch synthesis is realized by impregnating a conventional supported Fischer-Tropsch catalyst in which at least part of the catalytic metal is in its reduced metallic state under a non-oxidizing atmosphere with a solution of at least one member selected from the group consisting of ammonium salts, alkyl ammonium salts and weak organic acids, optionally in combination with ammonia, oxidizing in the presence of the impregnating solution, and activating the catalyst by contact with a hydrogen-containing gas at elevated temperatures.
The process of the present invention is useful to enhance the properties of any catalyst, including those commercially available and is particularly useful for catalysts that, regardless of the source, have been poorly prepared or poorly reduced and, as a result, do not have the proper dispersion of metallic catalyst on the support. Such catalysts may generally be referred to herein as catalyst precursors which term also includes suitable supports that have been impregnated with one or more metals prior to activation. The term xe2x80x9ccatalystxe2x80x9d as utilized herein includes such precursors.
In accordance with the present invention, the catalyst is initially reduced to convert at least a portion thereof to its metallic state. This is carried out by contacting with a hydrogen-containing gas at elevated temperatures, i.e. from about 200xc2x0 C. to 600xc2x0 C., preferably from about 250xc2x0 C. to 400xc2x0 C. Typically, the hydrogen pressure for this treatment would be from atmospheric to about 100 atm, preferably from atmospheric to about 30 atm and gas hourly space velocities of from about 100 V/Hr/V to about 40,000 V/Hr/V, preferably from about 1,000 V/Hr/V to about 20,000 V/Hr/V, expressed as standard volumes of the gaseous carbon monoxide and hydrogen mixtures (25xc2x0 C., 1 atm) per hour per volume of catalyst, respectively. Because of the metallic state of at least a portion of the catalyst after reduction, it is necessary to recover the catalyst under a non-oxidative atmosphere since some catalysts have a tendency to be pyrophoric. By non-oxidative is meant that the atmosphere need not be a pure inert gas, but may comprise an oxidative gas so long as no substantial oxidation of the catalyst takes place during the recovery thereof. One or a mixture of art-recognized non-oxidative gases, such as nitrogen, argon and the like may be utilized to create such atmosphere, with nitrogen being preferred.
In accordance with the present invention, the reduced catalyst is impregnated by contacting with a solution of at least one of a weak organic acid, an ammonium salt and an alkyl ammonium salt, optionally in combination with ammonia, and thereafter oxidized in the presence of the impregnating solution. The choice of solvent is dependent primarily on the capacity thereof to solubilize the ammonium salts, alkyl ammonium salts, or solubilize or be miscible with the weak organic acids as will be described below. The solvent is preferably water, however, other solvents, e.g. certain organic solvents, may be combined therewith provided that they are miscible with water and do not introduce any known catalytic poison. Mixtures of water and immiscible organic solvents can be utilized as well as mixtures of water with solvents in combination with suitable dispersing or emulsifying agents present to form a continuous phase, i.e. an emulsion. Such other suitable liquids include hydrocarbons, particularly those derived from the Fischer-Tropsch synthesis, dense fluids, for example, supercritical fluids such as liquid phase light hydrocarbons, i.e. C3-5, alkanes, cyclopentane and the like. Preferred mixed liquids include, without any intended limitation, water/lower alkanols, water/Fischer-Tropsch products, and water/alkanols/alkanes.
The weak organic acids, ammonium salts or alkyl ammonium salts utilized in the impregnating solution are preferably those that are easily removable from the catalyst without the deposition of any material that might have a deleterious effect on the performance of the catalyst. Examples of the latter would be materials containing halogens, sulfur, phosphorus and the like.
By alkyl ammonium salts, we include mono-, di-, tri- and tetra-alkyl ammonium salts or any mixture thereof. In a non-limiting preferred embodiment, combinations of the salts with ammonia are utilized and the concentration of ammonia in the solution does not exceed about five moles per liter. Suitable weak organic acids for the subject process are carboxylic acids having the general formula Rxe2x80x94(COOH)n wherein n is 1-3 and R represents a cyclic or aliphatic, saturated or unsaturated moiety that may be substituted with one or more nitro, amino, hydroxyl or alkoxyl groups. Specific examples of suitable acids include, without intended limitation, formic acid, acetic acid, citric acid, succinic acid, malonic acid, propionic acid, butyric acid, valeric acid, caproic acid, glutaric acid, adipic acid, lactic acid, benzoic acid, phthalic acid, salicylic acid, ascorbic acid, oxalic acid and the like. Suitable ammonium or alkyl ammonium salts include, without intended limitation, the nitrate, cyanide, carbonate, and carboxylates. The term xe2x80x9ccarboxylatesxe2x80x9d as utilized herein includes salts of the weak organic acids as defined above. Preferred examples of suitable acids and salts include, without intended limitation, acetic acid, citric acid, ammonium acetate and ammonium nitrate. While combinations of more than one of these acids or ammonium salts or alkyl ammonium salts could be utilized, in general it is preferred to utilize them individually.
The concentration of each of the constituents of the impregnating solution will depend on a number of factors including the solubility or miscibility of the weak acid, salt or salts, the volume of liquid utilized, the metal loading of the catalyst and the like. Optionally, the impregnating solution also contains ammonia in an amount up to twice the molecular equivalent of the at least one salt, said amount in any event not exceeding about five moles per liter of the impregnating solution. In general, the impregnating solution will contain from about 1% to about 30%, preferably from about 5% to about 15%, by weight of the ammonium or alkyl ammonium salt, and up to about 5 moles per liter of ammonia. In a preferred embodiment having ammonia present, the concentration thereof is chosen according to the following equation:
[NH3]/(nxe2x88x92[(NH4+)nX])xe2x89xa61
wherein X is the anion of the salt, n is the charge of the anion of the salt and the bracketed expressions are concentrations in moles per liter of the impregnating solution.
The amount of the weak acid, ammonium salt or alkyl ammonium salt present, under any conditions, is less than the amount that would be required to convert all of the catalyst metals present to their corresponding salts. The impregnating solution of the ammonium or alkyl ammonium salt or salts may be prepared by simply dissolving it in the selected solvent, or by combining solution of suitable reactants that will form it in-situ, e.g. acetic acid and aqua ammonia to obtain an ammonium acetate solution.
The impregnation will typically be carried out until the supported catalyst substrate has absorbed a volume of impregnating solution equal to at least about 10% of its calculated pore volume, preferably to where conditions of incipient wetness are attained. By incipient wetness is meant that the substrate catalyst has adsorbed an amount of solution generally equivalent to its calculated pore volume. Pore volume is a discernible quantity that can be measured directly or indirectly by known techniques such as porosimetry. The volume of impregnating solution contemplated will vary from 10% to 1,000% of the calculated pore volume of the catalyst. Preferably, the volume of treatment solution will be from 30% to 200%, most preferably from about 70% to 100% of the calculated pore volume of the catalyst.
The impregnating solution will remain in contact with the catalyst for from 1 minute to 24 hours, preferably from about 5 to 120 minutes. The time required for the treatment will vary depending on factors such as the metal loading of the catalyst being treated, the quantity thereof, the composition and volume of the impregnating solution, the reactor configuration and the like. The treatment is carried out at a temperature from about 0xc2x0 C. to about 100xc2x0 C., preferably from room temperature, i.e. 20xc2x0-25xc2x0 C., to about 80xc2x0 C. The pressure is not particularly critical and can be from 0.1 to 100 atmospheres, with atmospheric pressure being preferred. It is important, however, that the impregnation be carried out under a non-oxidative atmosphere as defined above, preferably an inert atmosphere.
Once the reduced, supported catalyst has absorbed the desired volume of impregnating solution, it undergoes oxidation in the presence of the impregnating solution. It has been found in accordance with the present invention that the oxidation of the catalyst is significantly enhanced by the presence of the constituents of the impregnating solution. Without wishing to be bound by any particular theory, it is believed that the presence of the weak acid, ammonium or alkyl ammonium salt or salts allows the formation of and enhances the solubility of complexes of the catalyst metal, e.g. Co2+ or Co3+. The presence of ammonia promotes the formation of such complexes as well. The action of the weak acid, ammonium salt, alkyl ammonium salt or mixtures thereof in enhancing the solubility of the complexes promotes their distribution within the pores of the catalyst surface. This dispersing, or re-dispersing, of the catalyst metal enhances the properties of the catalyst upon activation as will be described below.
The oxidation of the catalyst is carried out by contacting with an oxidant-containing gas. As discussed above, the ammonium salt, alkyl ammonium salt or mixtures of one or more of such salts may be itself an oxidant, e.g. ammonium nitrate. Although such an ammonium salt or alkyl ammonium salt will produce some oxidation of the catalyst metal during the impregnation, the desired level of oxidation may not occur until the oxidant gas is brought into contact with it. The oxidant gas may be oxygen, air, ozone, nitrogen oxides or other gaseous oxidant, with air or a mixture of oxygen and an inert gas being preferred. Generally, the concentration of the oxidant, preferably oxygen, in the oxidant gas will be between 10 ppm and 21 vol %, preferably between 1% and 21 vol % by volume. Typically, the treatment gas pressure would be from about 0.1 atm to about 100 atm, preferably atmospheric to about 10 atm, and the gas hourly space velocities would be from about 10 V/Hr/V to about 10,000 V/Hr/V, preferably from about 100 V/Hr/V to about 1,000 V/Hr/V, expressed as standard volumes of the gas or gas mixtures (25xc2x0 C., 1 atm) per hour per volume of catalyst, respectively.
The oxidation is typically exothermic and care must be taken to maintain the temperature below about 100xc2x0 C., preferably below about 80xc2x0 C. This is generally carried out by adjusting the concentration of the oxidant in the treatment gas to thereby prevent significant evaporation of the impregnating solution. A gradual increase in the oxidant concentration in the treatment gas has been found to provide an effective means of controlling the exotherm. Optionally, incremental replacement of the impregnating solution may be carried out during the oxidation. This serves the dual purpose of preventing the catalyst from drying out and aiding in controlling the exotherm through the cooling effect of evaporation. The use of an oxygen-containing gas in combination with an oxidant salt as the ammonium salt, e.g. ammonium nitrate, is particularly effective in the oxidation of the catalyst.
The oxidation step is generally carried out until a discernible change takes place in the catalyst and/or the reaction environment. Changes in the catalyst will include changes in color. Changes in the reaction atmosphere will include a cessation of the evolution of ammonia and/or the diminishing of the exotherm. This generally will require from about 1 to 120 minutes. Once the oxidation is concluded, the catalyst particles are preferably dried, typically at a temperature of from about 50xc2x0 C. to 150xc2x0 C., optionally with a gas sweep.
The treated catalyst particles are activated by reduction with a hydrogen-containing gas at elevated temperatures, i.e. from about 200xc2x0 C. to 600xc2x0 C., preferably from about 250xc2x0 C. to 400xc2x0 C. Hydrogen partial pressure during the reduction would range from about 1 to 100 atmospheres, preferably from about 1 to 40 atmospheres, and the gas hourly space velocities would be from about 100 V/Hr/V to about 40,000 V/Hr/V, preferably from about 1,000 V/Hr/V to about 20,000 V/Hr/V, expressed as standard volumes of the gas or gas mixtures (25xc2x0 C., 1 atm) per hour per volume of catalyst, respectively. The resulting supported catalyst particles enhanced in accordance with the present invention have been found to have a significant portion of their original activity restored, both in terms of production of the desired hydrocarbons and in methane selectivity. However, if it is decided for whatever reason that the activity of the catalyst is not sufficiently enhanced, the foregoing steps may be repeated, beginning with the impregnation step.
As an optional step in the subject process, the supported catalyst described above is calcined under an oxidant-containing atmosphere prior to the activation step. The atmosphere is preferably air, but may be an inert atmosphere containing a controlled amount of oxygen, e.g. such as would be produced as a product gas stream or a waste gas stream from an air separation plant. Such controlled oxidant-containing atmospheres would contain from 10 ppm to 21% by volume, preferably from about 1% to 21% by volume, oxygen with the remainder being a non-oxidative gas, preferably an inert gas, such as nitrogen. The gas flow in the furnace is from about 100 to 10,000, preferably from about 1,000 to 5,000 GSHV. The calcination is carried out at elevated temperatures, i.e. from about 150xc2x0 C. to about 600xc2x0 C., preferably from about 200xc2x0 C. to 450xc2x0 C., for from about 1 to 8 hours, preferably from 1 to about 4 hours. Suitable apparatus for the calcining step may be a rotary calciner such as described in Perry""s chemical Engineer""s Handbook, Seventh Edition, Chapter 12, McGraw-Hill, N.Y. (1997), a fluidized processor as will be described below, or an HCS reactor itself.
It is a further optional step within the scope of the present invention to passivate the treated catalyst after the activation with a hydrogen-containing gas has been carried out. The passivation may be carried out by contacting the catalyst with a gas containing carbon monoxide, or carbon monoxide and hydrogen, under conditions such that carbon monoxide does not significantly decompose and is not hydrogenated to a material degree. Such conditions, for example, would be a temperature below about 150xc2x0 C., preferably between about 25xc2x0 C. and 100xc2x0 C., and pressure below about 20 atm, particularly between about 1 and 10 atm and the gas hourly space velocities would be from about 1 V/Hr/V to about 1,000 V/Hr/V, preferably from about 10 V/Hr/V to about 500 V/Hr/V, expressed as standard volumes of the gas or gas mixtures (25xc2x0 C., 1 atm) per hour per volume of catalyst, respectively. It will be appreciated that some decomposition or hydrogenation, respectively, of the carbon monoxide may take place regardless of the precautions taken by the operator. However, it has been found that, typically, significant decomposition/hydrogenation will not take place wherein the concentration of carbon monoxide or carbon monoxide and hydrogen in the feed gas does not exceed about 5% by volume. Other passivating agents include, for example, traces of oxygen or carbon dioxide.
The treatment process in accordance with the present invention may be carried out in a series of apparatus particularly adapted to a specific step or steps, but preferably is carried out in a single processor device that can impart mixing and fluidization to the process. It would be configured to enhance heat transfer, mixing liquid-contacting, and gas solid transfer. Examples of suitable processors are gas fluidized beds, vibro-fluidized beds, mechanical blenders, e.g. double cone, vee, ribbon and the like and mixers such as plow, planetary, paddle and the like. These devices fluidize the processed material by passing a gas directly through it, by mechanical agitation or by a combination of both actions. Processing in such a device causes the material being treated to attain fluid-like properties resulting in intimate contact between each particle and the gas stream thus creating an extremely efficient mass and heat transfer. A device that provides at least mechanical fluidization is particularly preferred since, although both a slurry and a powder can be made to readily flow, during the drying process from one to the other, the material will pass through what is termed the xe2x80x9cmud stagexe2x80x9d where it is extremely difficult to fluidize. Hence, if the amount of solution utilized for the impregnation treatment is such that the material approaches or achieves the mud stage, a processor should have at least mechanical and, preferably, both mechanical and gas fluidization.
A preferred processor for carrying out the subject process is the plow mixer, a device with a jacketed horizontal cylinder with an axial agitator shaft containing several sets of blade or triangular agitators. Such a device will typically also have both gas and liquid inlets and outlets as well as an inlet and outlet for the solid material being processed. While this is a preferred device, any comparable mixer possessing the foregoing capabilities could be utilized as well provided that it has the capacity to fluidize the material from the mud stage to a dry, flowable material. Such a device will also facilitate the subsequent contact with hydrogen containing gas at elevated temperatures. A mechanical mixer, such as a plow mixer, is advantageous in that the liquid may be added while the material is in a fluidized condition. Because the mixer has inlet and outlet means for gas, when the material has been impregnated to the desired degree, the subsequent oxidation with a gaseous oxidant may be affected therein as well. At the completion of the low temperature oxidation step, as indicated by the cessation of the exotherm, the material may remain if the processor, or may be removed for further processing, for example, drying and calcination steps discussed above. All of these operations may be carried out in the processor if desired.
The final activation of the material to form an active catalyst can be carried out in a fluidized processor as described above. A larger variety of devices may be utilized for this step, however, since the material does not pass through a mud phase, hence gas fluidizers can be utilized for the excellent solid-gas contact they provide. For the same reason, a gas fluidizer may be utilized for the optional passivation step described above as, again, the material does not transcend through a mud phase. It can be appreciated, that a series of varied devices can be utilized to carry out the process of the present invention, which may be advantageous for large-scale operations. However, as described above, it is also possible to carry out the entire process of activation of the supported catalyst in a mechanical fluidizer having the capabilities of solid, gas and liquid transfer.
It is understood that various other embodiments and modifications in the practice of the invention will be apparent to, and can be readily made by, those of ordinary skill in the art without departing form the scope and spirit of the invention as described above. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the exact description set forth above, but rather that the claims be construed as encompassing all of the features of patentable novelty that reside in the present invention, including all the features and embodiments that would be treated as equivalents thereof by those skilled in the art to which the invention pertains. The invention is further described with reference to the following experimental work.